The use of metal drive chains and sprockets in drive systems to transfer mechanical power from one moving element of a machine to another moving element is very well known. Drive chains are commonly used in machines powered by electric motors or actuators, internal combustion engines, human-power and the like. A shortcoming of conventional metal drive system components, such as chains and sprockets, is that they require periodic lubrication which attracts contamination that ultimately erodes chain performance and useful life.
It is well understood that the lubricant is problematic in many manufacturing processes that are sensitive to contamination. For example, in the manufacture of photographic sensitized goods, contamination of the product by debris and lubricant from chain drive mechanisms is an issue which can affect product yield. Similarly, in the food packaging industry, contamination of the food product or package by chain lubricant or debris is unacceptable. Chain drive systems in bicycles require lubrication to lower friction thereby reducing the work required of the rider and also to reduce chain wear. Unfortunately for off-road bicycle applications, chain lubricants pick up and hold abrasive grit from the environment which itself causes excessive wear and abrasion and shortens chain life. An associated problem is chain ring (sprocket) wear. In high-performance bicycle applications, chain rings require replacement when their tooth height equals the tooth-to-tooth separation along the chain ring.
In some applications, for example, chains for high performance bicycles, chain stretch is a recognized problem, and is an indication of the end of useful chain life. Another problem associated with high-performance bicycle chain relates to unsmooth shifting when changing gear ratios. The problem has its origins in friction at both chain ring and rear sprocket because of side loading.
The problems associated with wear, abrasion, friction, stretch and contamination described above could be reduced or eliminated by the use of certain ceramic chains and sprockets/chain rings drive systems having the characteristics of high surface hardness, high bulk toughness and low coefficient of friction. Such components would exhibit long life because of low wear and low stretch, would not require lubrication and would be smooth in operation and shifting.
The use of ceramics in chains in the prior art has been limited. Bottger et al, WO 9413525 describe a metal crawler chain for tracked vehicles that incorporates ceramic bushes. Only the bushes are of ceramic (optionally) and the chain is in the form of a moving track which communicates with the earth and so does not transfer power from one moving element to another as in the present invention. Curtain and Stephens, U.S. Pat. No. 4,582,972 describe a chain feed mechanism for induction heat furnaces. The chain consists of alternating links of stainless steel and ceramic. Power is applied to the chain at the steel links only. Japanese patent 59218262 of Kumamoto describes a method of producing ceramic chains which consist of simple interlocking loop links. The chain of Kumamoto is unsuitable for use with the chain rings or sprockets which are related to the present invention, nor are the materials of Kumamoto suitable for the present invention. German patent 3005349 due to Lemmer describes the use of plurality of ceramic balls or links in the manufacture of printed circuit boards. The chain is laid down to cover circuit board components so as to hold them in place during wire trimming and soldering. The chain of Lemmer is not suitable for drive chain.
Our experience indicates that ceramic materials may have some unexpected advantages in such drive mechanism components, although the prior art currently does not support this conclusion. This is because most of the conventional high performance ceramics are extremely brittle. An example of a material having good hardness and strength is monolithic cubic spinel, however, this material is also highly brittle and is unusable for structural applications. Thus skilled artisans are more inclined to experiment with alternative metallic components in drive mechanisms. Repeated sliding of two surfaces of metal parts, as in this specific case of surfaces of chain links, separator rings and the sprockets, usually leads to excessive wear and abrasion of those surfaces leading to the loss of materials, contaminating the environment from the debris, and also creating a gap between the different components of the drive mechanism. This gap leads to the loss of power, and in some cases jamming and or breakage of the drive mechanism.
Therefore, a need persists for improved drive chain, and sprockets and method of making same so that the drive mechanism will have superior wear and abrasion resistance while being cost effective and easy to manufacture.